@@ -41,8 +41,7 @@ struct kmem_cache *xfs_buf_cache;
*
* xfs_buf_rele:
* b_lock
- * pag_buf_lock
- * lru_lock
+ * lru_lock
*
* xfs_buftarg_drain_rele
* lru_lock
@@ -220,14 +219,21 @@ _xfs_buf_alloc(
*/
flags &= ~(XBF_UNMAPPED | XBF_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD);
- spin_lock_init(&bp->b_lock);
+ /*
+ * A new buffer is held and locked by the owner. This ensures that the
+ * buffer is owned by the caller and racing RCU lookups right after
+ * inserting into the hash table are safe (and will have to wait for
+ * the unlock to do anything non-trivial).
+ */
bp->b_hold = 1;
+ sema_init(&bp->b_sema, 0); /* held, no waiters */
+
+ spin_lock_init(&bp->b_lock);
atomic_set(&bp->b_lru_ref, 1);
init_completion(&bp->b_iowait);
INIT_LIST_HEAD(&bp->b_lru);
INIT_LIST_HEAD(&bp->b_list);
INIT_LIST_HEAD(&bp->b_li_list);
- sema_init(&bp->b_sema, 0); /* held, no waiters */
bp->b_target = target;
bp->b_mount = target->bt_mount;
bp->b_flags = flags;
@@ -502,7 +508,6 @@ int
xfs_buf_cache_init(
struct xfs_buf_cache *bch)
{
- spin_lock_init(&bch->bc_lock);
return rhashtable_init(&bch->bc_hash, &xfs_buf_hash_params);
}
@@ -652,17 +657,20 @@ xfs_buf_find_insert(
if (error)
goto out_free_buf;
- spin_lock(&bch->bc_lock);
+ /* The new buffer keeps the perag reference until it is freed. */
+ new_bp->b_pag = pag;
+
+ rcu_read_lock();
bp = rhashtable_lookup_get_insert_fast(&bch->bc_hash,
&new_bp->b_rhash_head, xfs_buf_hash_params);
if (IS_ERR(bp)) {
+ rcu_read_unlock();
error = PTR_ERR(bp);
- spin_unlock(&bch->bc_lock);
goto out_free_buf;
}
if (bp && xfs_buf_try_hold(bp)) {
/* found an existing buffer */
- spin_unlock(&bch->bc_lock);
+ rcu_read_unlock();
error = xfs_buf_find_lock(bp, flags);
if (error)
xfs_buf_rele(bp);
@@ -670,10 +678,8 @@ xfs_buf_find_insert(
*bpp = bp;
goto out_free_buf;
}
+ rcu_read_unlock();
- /* The new buffer keeps the perag reference until it is freed. */
- new_bp->b_pag = pag;
- spin_unlock(&bch->bc_lock);
*bpp = new_bp;
return 0;
@@ -1090,7 +1096,6 @@ xfs_buf_rele_cached(
}
/* we are asked to drop the last reference */
- spin_lock(&bch->bc_lock);
__xfs_buf_ioacct_dec(bp);
if (!(bp->b_flags & XBF_STALE) && atomic_read(&bp->b_lru_ref)) {
/*
@@ -1102,7 +1107,6 @@ xfs_buf_rele_cached(
bp->b_state &= ~XFS_BSTATE_DISPOSE;
else
bp->b_hold--;
- spin_unlock(&bch->bc_lock);
} else {
bp->b_hold--;
/*
@@ -1120,7 +1124,6 @@ xfs_buf_rele_cached(
ASSERT(!(bp->b_flags & _XBF_DELWRI_Q));
rhashtable_remove_fast(&bch->bc_hash, &bp->b_rhash_head,
xfs_buf_hash_params);
- spin_unlock(&bch->bc_lock);
if (pag)
xfs_perag_put(pag);
freebuf = true;
@@ -80,7 +80,6 @@ typedef unsigned int xfs_buf_flags_t;
#define XFS_BSTATE_IN_FLIGHT (1 << 1) /* I/O in flight */
struct xfs_buf_cache {
- spinlock_t bc_lock;
struct rhashtable bc_hash;
};
xfs_buf_cache.bc_lock serializes adding buffers to and removing them from the hashtable. But as the rhashtable code already uses fine grained internal locking for inserts and removals the extra protection isn't actually required. It also happens to fix a lock order inversion vs b_lock added by the recent lookup race fix. Fixes: ee10f6fcdb96 ("xfs: fix buffer lookup vs release race") Reported-by: "Lai, Yi" <yi1.lai@linux.intel.com> Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com> --- Changes since v1: - document the initial buffer state vs lockless lookups fs/xfs/xfs_buf.c | 31 +++++++++++++++++-------------- fs/xfs/xfs_buf.h | 1 - 2 files changed, 17 insertions(+), 15 deletions(-)